Theoretically yes but by then you wont get 32bit OS's anyway. You could in theory keep a machine running with a 32bit OS until you need that sort of on board Ram on a GPU but i recon it would need to be left in a couple of wills first
Also just for the sake of it the machine wouldnt have any actual Ram if the GPU took up all the address space so wouldnt work anyway. Im not 100% sure but i think that the GPU gets given space first and the system Ram is addressed last.
so if you are running a 2gb card now you are limiting your OS to 1.2 ish of Ram.
The limit on 32bit systems is 4096mb this is due to address length of the os. Think of it this way of there are only 2 blank spaces on a piece of paper the highest number you can write in is 99. And that limit is caused by the os so switching the os to 64 bit solves the problem for all aspects with its limit of 128gb